The present invention relates to a golf ball capable of exhibiting a stable flying performance by highly symmetrically, equally arranging dimples on the surface of the ball by a spherical octahedron arrangement method.
A large number of dimples are arranged on the outer surface of a golf ball for increasing the flying performance of the golf ball. The flying performance of a golf ball, however, varies depending on the rotational direction (the latitudinal direction, longitudinal direction, or the intermediate direction therebetween) of the golf ball, which differs depending on a hitting point of a ball. The variation in rotational direction of the golf ball depending on a hitting point of a ball is mainly due to the distribution of the dimples arranged on the surface of the ball. From this viewpoint, various methods have been proposed to reduce a variation in flying performance of a golf ball by enhancing the uniformity as much as possible in arrangement of dimples on the surface of the golf ball.
With respect to such dimple arrangement, from the practical viewpoint, there has been generally used a method of arranging dimples on the spherical surface of the golf ball by assuming the spherical surface of the golf ball as a spherical polyhedron such as an icosahedron or an octahedron and using, as dimple arrangement units, spherical triangles constituting the spherical octahedron, on each of which a specific number of the dimples are equally arranged.
FIG. 13 shows an example of spherical regular octahedron arrangement. Referring to FIG. 13, the spherical surface of the golf ball is equally divided into eight spherical triangles T forming a spherical octahedron by a longitudinal line xe2x80x9caxe2x80x9d (0xc2x0 to 180xc2x0), a longitudinal line xe2x80x9cbxe2x80x9d (90xc2x0 to 270xc2x0), and an equatorial line. Dimples of the total number of 368 are arranged on the spherical surface of the golf ball by using as dimple arrangement units, the spherical triangles T on each of which 46 of four types of dimples different in diameter, concretely, large dimples D1, medium dimples D2, small dimples D3, and minimum dimples D4 are equally arranged. In the figure, character xe2x80x9cexe2x80x9d designates a pole.
In this example, on each of three sides of the spherical triangle T, any dimple is not formed but a land is formed for simplifying the works of molding the golf ball. To be more specific, on each of three great circles composed of the longitudinal lines xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d and the equatorial line xe2x80x9ccxe2x80x9d, any dimple is not formed but a land is continuously formed.
For such a golf ball, an aerodynamic effect of the dimples differs between the case where the golf ball rotates in the direction along either of the three great circles a xe2x80x9cbxe2x80x9d and xe2x80x9ccxe2x80x9d on which the land is continuously formed and the case where the golf ball rotates in the direction deviated from any one of the great circles, with a result that there arises a problem that the flying performance of the golf ball varies depending on a hitting point of the golf ball.
To solve such an inconvenience and to increase the uniformity of the arrangement of dimples, there has been proposed a spherical octahedron arrangement method in which one or a plurality of dimples are arranged on a side, extending in the longitudinal direction, of a spherical triangle. In this case, since each dimple located on the side, extending in the longitudinal direction, of the triangle must be in a left-right symmetric relationship with respect to the side of the triangle, the center of the dimple is located on the side of the triangle. That is to say, in this case, the dimple is equally divided into two parts by the side of the triangle.
On the other hand, generally, any dimple is not arranged on a side, corresponding to the equatorial line, of the spherical triangle. The reason for this is due to the fact that since the equatorial line is generally taken as a great circle corresponding to a mold parting plane, if any one of dimples is located on the equatorial line, it is difficult to perform a work of finishing the molded golf ball because of the structure of a mold for molding the golf ball.
Such a golf ball produced in accordance with the above-described proposed method, however, also has the problem that the flying performance of the golf ball varies depending on the rotational direction of the golf ball.
An object of the present invention is to provide a golf ball capable of highly symmetrically, equally arranging dimples on the surface of the ball by a spherical octahedron arrangement method, thereby exhibiting a stable flying performance irrespective of a hitting point of a ball.
To achieve the above object, according to the present invention, there is provided a golf ball including: a plurality of dimples arranged overall on the spherical surface of the golf ball by assuming the spherical surface of the golf ball as a spherical octahedron and using, as dimple arrangement units, eight spherical triangles constituting the spherical octahedron, on each of which a specific number of the dimples are arranged; wherein at least the four dimples are arranged on each of three sides of the spherical triangle; there is no great circle with which any one of the dimples does not intersect; and the total number of the dimples is in a range of 380 to 450.
In this golf ball, the dimples may be arranged on the surface of the ball in such a manner that one of four great circles formed by connecting associated ones of mid points of sides of the spherical triangles to each other is an equatorial line which substantially corresponds to a parting plane of a two-half mold for molding the golf ball, and the great circle corresponding to the equatorial line has no dimple whose center intersects with the great circle.
With this configuration, it is possible to significantly improve the aerodynamic characteristic of the golf ball as compared with a conventional golf ball, and to equalize the flying performance of the golf ball by significantly reducing a variation in flying performance of the golf ball due to a difference in hitting point between shots.
Further, according to the present invention, since the area of a portion, extending in the direction deviated from the equatorial line, of a parting plane of a two-half mold for molding the golf ball is small, the polishing width becomes narrow, with a result that the polishing amount becomes small, and since no burr occurs in each dimple, the polishing work becomes easy and also an undesirable deformation of each dimple located on the equatorial line can be prevented. As a result, the golf ball molded using such a mold is significantly advantageous in keeping the uniformity of the dimple effect (aerodynamic characteristic) of the golf ball.